Conjugated linoleic acid (CLA) is a conjugated isomer of linoleic acid (LA), which is an essential fatty acid that is a naturally occurring fatty acid found in the breast milk or muscle of ruminants in a trace amount. CLA is a general term used to name positional and geometric isomers of linoleic acid having conjugated double bonds in cis- or trans-configuration. Among those CLA isomers, physiologically functional cis-9, trans-11 octadecadienoic acid and trans-10, cis-12 octadecadienoic acid are specifically referred to as the CLA. The CLA is excellent in reducing incidence of sclerosis of the artery (Artery, 1997, 22:266-277), enhancing immunogenicity (J. Nut., 1999, 129:32-38) and anti-cancer activity (Anticancer research, 1997, 17:969-973), promoting growth (J. Nut., 2000, 130:2981-2989) and therapeutic effects with respect to diabetes or other diseases. Further, the CLA has been reported to suppress obesity by reducing body fat (Am. J. Physiol., 1998, 275:R667-R672). By virtue of such properties, the CLA can be advantageously used as the effective component of functional food and pharmaceutical products.
In general, human ingest glyceride of CLA through foods prepared by esterification of CLA and glycerol. These examples are disclosed in U.S. Pat. No. 6,432,453 and US Pat. Publication No 2002/0147356 etc.
Glycerides synthesized by an esterification reaction are classified into monoglycerides (MG), diglycerides (1,2-DG, 1,3-DG, 2,3-DG), and triglycerides (TG) according to the degree of substitution of hydroxyl group.
Diglycerides are fat compositions in which fatty acid(s) and 1-, 2-, or 1- and 3-position glycerin(s) are bonded by an esterification reaction and are classified differently from ordinary fats called triglycerides.
Recently, it has been reported that diglyceride has substantially the same digestion and absorption mechanisms as ordinary neutral fat and does not cause adverse physiological effects when ingested, such as a rise in the neutral fat level in human serum or accumulation of body fat, because little diglyceride is resynthesized to become neutral fat. Accordingly, research into preparation methods of such diglyceride is continuously being carried out.
But as like triglyceride, the diglyceride is hydrolyzed by various facts during keeping or processing (eg. Cooking), and as the result, free fatty acid comes into being, and the free fatty acid produces offensive smell and toxic materials via oxidation, decomposition and composition. Also, rancidity such as color change, increase of free fatty acid, increase peroxidant, change of taste and odor happens by heating cooking. Therefore antioxidant in fat composition is indispensable.
These antioxidants mean material that prevent or delay change of odor, taste, color in food, medical, cosmetic and rancidity in fat composition, and there are synthetic antioxidant and natural antioxidant.
The examples of synthetic antioxidant are t-butylated hydroxytoluene (BHT), t-butylated hydroxyanisol (BHA), t-butylated hydroxyquinone(TBHQ), aminodiphenylamine, etc, and the examples of natural antioxidant are tocopherol, rosemaric acid, catechol, caffeic acid, ascorbic acid, etc.
The afore-mentioned synthetic antioxidants such as t-butylated hydroxytoluene (BHT), t-butylated hydroxyanisol (BHA) have the problem of decomposing by heat, and giving rise to tumor, so the synthetic antioxidants are unreasonable in view point of stability. Therefore the usages of synthetic antioxidants have been decreased, while natural antioxidants have been preferred recently.
Various researches in extracting antioxidant from natural plant and using the same are actively progressing (Natural antioxidant from residual sources, Food Chem, 72, 145˜171, 2001), and the representative natural antioxidant extracted from natural plant are rosemary extracts, green tea extracts, etc.
Also, potato peels extract (Utilization of potato peels extract as a natural antioxidant in soy bean oil, Food Chem, 85, 215˜220, 2004), olive mill wastewater (The use of polyphenolic extract, purified hydroxytyrosol and 3,4-dihydroxyphenyl acetic acid from olive mill wastewater for the stabilization of refined oils: a potential alternative to synthetic antioxidant. Food Chem, 93, 197˜204, 2005), and grape seeds (Effect of heating conditions of grape seeds on the antioxidant activity of grape seed extract, Food Chem, 97, 472˜479, 2006) shows relatively high antioxidant effect.
But, the above natural antioxidants extracted from natural plants are too expensive, and show lower antioxidant effect than synthetic antioxidant, and shows uneven antioxidant effect regarding different products, and have bad heat stability restricting the usage.
Therefore, research on fatty acid comprising plant-extracted antioxidant of improved stability and antioxidant effect is in need.